Process of purifying gases containing sulfur dioxid.



G. ESOHELLMANN.

rnoonss or PURIPYING (mans UONTAINING SULFUR. 1110x112. APPLICATIONFILED MAY 8,. 1907.

900,500, Patented Oct. 6, 1908.

fif'a'lrzeaa ea I 710621607- UNIT STATES PTET FQE.

GEORG ESOHELLMANN, OF ST. PETERSBURG, RUSSIA.

PROCESS OF PURIFYING GASES CONTAINING SULFUR DIOXID.

To all whom it may concern:

Be it known that I, Gnonc ESGHELLMANN, a subject of the King of GreatBritain, residing at St. Petersburg, Russian Empire, have inventedcertain new and useful Improvements in Processes of Purifying GasesContaining Sulfur DioXid, of which the following is a specification.

In the practice of manufacturing anhydrous sulfuric acid by the contactprocess from sulfur (lioXid derived from pyrite, the gas must as is wellknown be subjected to a thorough purification for the purpose ofprotecting the apparatus and more particularly the contact mass.Heretofore efforts to purify these gases have been directed mainly toeffecting the complete separation of the vapors of hydrated sulfuricacid, and the finely distributed impurities containing iron, manganese,copper, nickel, arsenic, antimony, phosphorus, mercury, lead, zinc,bismuth, calcium, selenium, fiuorin, etc;; Chlorin commonly occurs as aninjurious constituent of such gases, but its separation there from is anunsolved task.

According to this invention chlorin is completely separated from the gascurrent by subjecting the same, after the vapors of hydrated sulfuricacid have been carefully removed, to the action of hydroxids of thealkali or alkaline earth metals. Under these conditions bisulfites areformed, and the chlorin is removed through their agency.

It has been heretofore proposed to treat the impure hot sulfur dioxidwith steam for the purpose of precipitating vapors of sulfuric acid, andafter cooling to wash the gas with water for the purpose of removing theremaining sulfuric acid vapors, the water used for this purpose havingbeen mixed with sodium sulfite or similar compounds. It is evidenthowever that such method is ineffective for the removal of chlorin,inasmuch as the sulfite or bisulfite of sodium is immediatelytransformed into sulfate by the sulfuric acid. It follows that the gasespassing to the contact apparatus contain chlorin, which not only injuresthe contact mass but appears in the sulfuric acid produced; moreover aconsiderable quantity of sulfuric acid which always collects in thewashing apparatus is contaminated by the sulfate formed therein, and itsvalue is there by impaired. It is evident moreover that chlorin couldonly be removed by this process by adding to the water a purifying agentSpecification of Letters Patent.

Application filed May 8, 1907.

Patented Oct. e, 1908.

Serial No. 372,501.

of compound in such large proportion as would be required to combineboth with the sulfuric acid and with the chlorin contained in the gases.

The present invention offers the advantage that a relatively smallquantity of washing agent is required, and furthermore that the sulfuricacid contained in the gases, being removed before the washing of thegases by means of the hydroxids, is obtained directly in merchantableform.

According to the earlier process above mentioned the sulfuric acid isobtained as gypsum in case calcium hydroxid is employed for thepurification; this compound is not only practically without value butowing to its slimy character is liable to obstruct the washers. If analkali hydroXid is used a mixture of sulfate and chlorid is obtained insolution, and the sulfate can be recovered only after an expensiveconcentration and separation.

According to the present process the con sumption of the hydroxid of thealkali or alkaline earth metal is limited to the quantity required forthe absorption of the chlorin contained in the gases and of anyhydrochloric acid formed therefrom. The chlorid formed is readilysoluble even in case calcium hydroxid is employed as a washing agent,and is not mixed with sulfate derived from the sulfuric acid from theburner gases. The gases after treatment are free from the impuritieswhich are usually separated and are also entirely free from chlorin.

For a full understanding of the invention reference is made to theaccompanying drawing, showing a preferred form of apparatus in verticallongitudinal section.

Referring to the drawing, the gases pass from the burner to a dustchamber 1, provided with shelves 2, 2 upon which the coarser dust isdeposited, the thorough mixing of the gases in their passage over theshelves serving at the same time to bring about the complete combustionof the sulfur contained therein. The gases pass thence through a cooler3, wherein they are cooled by contact with water-cooled surfaces, andfurther portions of the dust are retained in the form of an easilyremovable slime; in this cooler a large proportion of the hydratedsulfuric acid vapors is condensed to sulfuric acid of about 52 Baum;this acid in practice is permitted to flow from the cooler in acontinuous stream.

The fine residual dust, as well as the residual sulfuric acid vapors,are then removed by conducting the gas from below through a coke filter4, hereinafter referred to as the coarse filter; this filter is inpractice con structed of two or more layers consisting of grains orfragments differing in size, the fragments being reduced in size in thedirection of the gas current, that is to say from below upward; theupper layer usually com prises grams approximately 10 millimeters.

in diameter. In this coarse filter a large proportion of the remainingvapors of sulfuric acid are condensed to sulfuric acid of about t-OBaum, which is permitted to flow off. The filter also retains any slimewhich may have been carried with the gas, as well as further portions ofthe dust.

The coarse filter 4 is preferably in practice so constructed that it canbe freed from dust by flushing with water from below, and means are alsoprovided for moistening the coke bed with water from either side inorder to effect the washing of the gases. For this purpose there arepreferably provided at the bottom of the filter uniformly distributedchannels made of brick on which the coke mass rests. Each of thesechannels can be flushed by itself, thus permitting uniform and thoroughwashing without the necessity of removing the coke mass. I11 practicetwo similar filters are provided and are so connected that either may beoperated independently, the gas being diverted to one of the filterswhenever it is necessary to clean the other.

From the coarse filter the gases enter the fine filter 5, of which alsotwo interchangeable units are provided. This fine filter contains a bedof coke composed of grains of approximately one millimeter in diameter,and serves to eliminate the very finest dust and vapor particles, in sofar as they may have traversed the coarse filter; the fine filter bedmay rest upon a bed of coarser particles as shown. In practice the gasenters the fine filter from above, so that the dust particles aredeposited in the upper portions of the coke bed. The cleaning of thefine filter is not affected by flushing, which is found in practice toentail the stoppage of the filter bed by slime, but by replacing thetopmost coke layer as far as it is found to be perme ated with dust, bya fresh layer, whereupon the filter is at once ready for use. Practicalexperience has shown that itis necessary to effect this cleansingprocess only about once a year, and that fine filters treated in thismanner can be used for years before it becomes necessary to refill them.Coke filtration as above described is found to be perfectly satisfactoryfor the continuous and thorough purification of large quantities ofpyrite gases.

The gases leaving the filter 5 are now conducted through a series ofwashing chann bers 6, 6, containing a dilute aqueous solution of analkali hydroXid, or milk of lime or other alkaline earth hydroxid.

In these chambers the corresponding alkali or alkaline earth sulfites orbisulfites are formed. and these enter at once into reaction with thechlorin contained in the gases, the chlorin combining with the base ofthe sulfite. The gas escaping from the washing chamber (3 found to beentirely free from chlorin, and after drying in the usual manner, as inthe drying tower T, is led to the contact apparatus.

In practice it is found preferable to use for the absorption of chlorinan alkaline earth hydroxid in solution or suspension and preferably milkof lime, for the reason that any traces of sulfuric acid passing throughthe filter are thereby instantly removed by combining to form insolublesulfates. The result of the process is to provide a gas which isabsolutely pure, and to ell'eet a greatincrease in the life of thecontact mass.

I claim:

1. The process of purifying burner gases which consists in separatingdust therefrom. cooling the gases and condensing sulfuric acid bycontact with cooled surfaces, removing residual dust and sulfuric acid\'apors by filtration, and thereafter subjecting the gases to a solutionof metallic hydroxid to absorb chlorin.

2. The process of purifying burner gases which consists in separatingdust therefrom, cooling the gases and condensing sulfuric acid bycontactwith cooled surfaces, removing residual dust and sulfuric acidvapors by filtration, and thereafter subjecting the gases to milk oflime to absorb chlorin and precipitate residual impurities.

In testimony whereof, I aflix my signature in presence of two witnesses.

GEORG ESCHEL L M ANN.

Vitnesses H. A. IJOYIAGUINE, AUG Mienis.

